The Influence of Positive and Negative Emotions on ...

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1Department of Psychology, Second University of Naples, Italy. 2International .... The timeline of the experiment follows: during the first 30s, the participant was.

DRAFT OF THE PAPER Riviello MT, Capuano V, Ombrato G, Baldassarre I, Cordasco C, Esposito A (2014) The Influence of Positive and Negative Emotions on Physiological Responses and Memory Task Scores. In Bassis S et al. (Eds), Recent Advances of Neural Network Models and Applications, vol. 26, 315-324, Springer Verlag, DOI 10.1007/978-3-319-04129-2, ISBN 978-3-319-04129-2, 2014. http://www.springer.com/engineering/computational+intelligence+and+compl exity/book/978-3-319-04128-5 Series: Smart Innovation, Systems and Technologies,

The Influence of Positive and Negative Emotions on Physiological Responses and Memory Task Scores M.T. Riviello1,2, V. Capuano1,2, G. Ombrato1, I. Baldassarre1, G. Cordasco1,2, and A. Esposito1,2 1 Department of Psychology, Second University of Naples, Italy International Institute for Advanced Scientific Studies (IIASS), Italy

2

{mariateresa.riviello, vincenzo.capuano, ivana.baldassarre,gennaro.cordasco, anna.esposito}@unina2.it [email protected]

Abstract. The present paper report results of a preliminary study devoted to investigate whether and how different induced emotional states influence physiological responses and memory task scores. Physiological responses, such as skin conductance (SCL) and heart rate (HR) values were measured from 32 university students, before, during and after they were elicited by video stimuli. The considered stimuli were able to induce positive, negative and neutral emotional states. The specific physiological activation patterns were identified and correlated with memory task scores, computed using the “Anna Pesenti” Story Recall Test (SRT). The results show significant changes in physiological values when positive (increase in HR values) and negative (increase in SCL values) emotional states are induced. Surprisingly, increased SCL values, associated to induced positive emotional states, affect the participant’s memory task scores. Keywords: emotion; physiological activation; memory task scores

1

Introduction

Emotion is defined as a complex state of feeling that results in physical and psychological changes able to influence thought and behavior. In particular, emotionality is associated with a range of phenomena including, among others, physiological arousal (activation), and cognitive processes as memory. Indeed, emotions involve the activation of behavioral dispositions implying bivalent reactions toward and away the stimulus that caused the arousal. These dispositions engage the Automatic Nervous System (ANS)[1-2], that governs involuntary actions, resulting, among others, in internal physiological changes such as electrical activities of the skin (skin conductance),respiratory activities, blood pressure, heart rate, sweat glands, reactions of the endocrine glands, chemical activities of blood. Sequeira et al. [3] sustained that any organ that is influenced by the ANS could be a potential index of mind activity. On this assumption, understanding physiological ANS indices may help the detection of emotional processing states. Several researches [4-8] showed that focused on specific physiological activation patterns underlay are related to specific emotional experience. Nevertheless, univocal associations between physiological activation patterns and specific emotional states have not yet been identified. For example, some studies identify different physiological activation features for sadness: when this emotion is correlated with crying, it is characterized by heart rate (HR) and skin conductance level (SCL) increasing values [9], whereas, with no crying, it can be observed an increase of the level values of both the physiological signals [10-11] or an increase of the HR and no changes in the SCL [12] values. Also studies on happiness [13-15] showed controversial data. In particular, the physiological response to happiness includes either increased HR [16-17], unchanged HR [18-19], or decreased HR values [20]. The physiological arousal dimension of emotion also represents a critical factor contributing to the emotional enhancement effect on memory [21].Thanks to the increasing accessibility of brain imaging techniques researches reveal that heightened physiological activity increases the probability of remembering, and this improvement is due to the amygdale activation that mediates consolidation of memory in other brain regions (for a review see [22]). In addition, there is evidence that memory can be enhanced even for the valence dimension of emotion, i.e. how positive or negative an event is. The studies [23] that investigate this dimension have found that items with positive or negative valence improve memory with the respect of neutral items, via modulation of distinct neural processes that are independent from the amygdala activation [24-26]. The Emotionally Enhanced Memory – EEM [27] is one of the most studied feature in psychology [27-30]. Scholars posit that emotional stimuli, both positive and negative, can facilitate the encoding process through attentional processes [31-33]. However, almost all the studies conducted on EEM involved memory task on arousing/emotional stimuli per se; whereas very few studies tested the so-called Easterbrook’s hypothesis [34],

which claims that attention is limited when people experience an high arousal not directly linked with the stimulus. The present study is a preliminary investigation aimed at observing whether and how positive and negative induced emotional states influence physiological responses and memory task scores. In particular, it estimates memory task performances on neutral stimuli (not arousing/emotional stimuli per se) after having induced arousal trough emotional stimuli separately. It examines changes in skin conductance (SCL) and heart rate (HR) values before, during and after individuals experienced emotional states of happiness, sadness and neutral. The abovementioned emotional states were elicited by showing video stimuli to the participants in the experiments. The main goal is to identify specific physiological emotional responses and to explore their possible effects on memory task scores, computed using the “Anna Pesenti” Story Recall Test (SRT) [35].

2

Experimental set-up

2.1

Materials

The materials used for the experiments are described below: a)

®PSYCHOLAB VD13SV, for measuring participants’ physiological values. This instrument was provided with two different sensors able to measure heart rate and skin conductance values.

b) Emotional videos, for evoking emotional states. Six video-clips were selected from the database of emotional evoking video stimuli described in [36]. Such database consists in assessed videos downloaded from YouTube. In particular, we selected one180 seconds (s) long video-clip for happiness inducing the positive emotional state 2 video-clips for sadness, assembled together in order to have a 180s long video-clip inducing the negative emotional state; and 3 video-clips assembled together to form a 180s long videoclip inducing the neutral emotional state. The emotional videos, i.e. happy and sad videos, contain the original audio-track (dialogues and music), whereas neutral videos are soundless. c)

“Anna Pesenti” Story [35], for evaluating memory performances. This story recall test is usually used in neuropsychology to evaluate memory impairments in Italian patients [37]. It is composed by 28 different mnemonic units. The original protocol requires an immediate and deferred recall: after the experimenter read the test twice, the patient (subject) is asked to recall the story immediately and after 15 minutes, during which he/she is involved in a distractive non-verbal task. A correction table is used to evaluate results, in terms of number of units recalled, according to years of schooling, age and gender of the subject. In this work participants were asked to recall the story

a single time, after the presentation of the emotional stimuli that in this case represents the non-verbal distractive task. 2.2

Participants

A total of 32 Italian university students (21 males and 11 females, age: 23,7 ± 3,4) were involved in the experiments. The participants filled and signed an agreement form declaring their voluntary participation and authorized the researchers to use the collected data for scientific purposes. 2.3

Procedure

Three experimental conditions were created according to the video stimuli presented, therefore, according to the emotional state induced: positive, negative, and neutral. The participants were partitioned into three groups so that 11 (8 males and 3 females) were assigned to positive, 10 (5 males and 5 females) to negative, and11 (8 males and 3 females) to neutral condition. The experimental procedure was stable for all the three condition and it is described below. Each participant sat in front of a computer and was connected to PSYCHOLAB VD13SV sensors. The timeline of the experiment follows: during the first 30s, the participant was able to read instructions 1 on the screen, so that he/she was informed about what it was going to be presented and how to proceed. Soon after, a fixation point (a crux in the middle of the screen) appeared for 180 s. This phase of the experimental procedure was used in order to induce a relaxation state in the participant and record physiological starting point data (baseline).Then, instructions2appeared on the screen for 5s. During this time the participant was asked to pay attention to the story he/she was going to listen for 2 times. In the following 55s, a clear recorded voice told the “Anna Pesenti” story twice. As soon as the voice stopped, instructions 3appeared on the screen for 5 s, informing the participant he/she was going to watch a video. Then the emotional video (positive, negative or neutral, according to the experimental condition the participant was assigned) was displayed on the screen for 180 s. At the end of the video presentation the participant was disconnected from the sensors and he/she was asked to recall the story he had listened to. A recorder stored the participant’s report, in order to compute the memory task scores as described in section 2.1. The experimental procedure timeline is summarized and displayed in Figure1. The two time intervals, depicted with black boxes in the figure, refer to the final 30 s of the fixation point time interval (considered as baseline) and the final 30 s of the emotional induction phase (considered as emotional state).Only the physiological (SCL and HR) values recorded during these two time intervals are used for the analysis. This approach, wildly used in literature [6, 38], was considered preferable because the considered data are related to a more complete relaxation state (baseline), and emotion induction (emotional state). Indeed, the autonomic nervous system deals with a lot of non-contingent activities as digestion, postural adjustment, thermoregulation,

etcetera, so care must be taken to ensure that the measurements are time-locked to the stimulus onset. Baseline 30s sssec. Instructions1

Emotional State

5s ssssss

180s ssssssssss

55s sec.

Instructions 2 Fixation Point

180s sec.

5s ssssss

free sec.

Instructions 3

Listening (2 times) to “Anna Pesenti” Story

Recall

Emotional Evoking Video

Fig. 1 Experimental procedure timeline. Each bracket indicates a specific phase of the experiment and its time duration. The physiological data used for the assessment are extracted during the two time intervals (Baseline and Emotional State) highlighted with black boxes.

3

Results

In order to evaluate the effect of the emotion induction on participants’ physiological activity paired samples t-tests were computed comparing baseline and emotional state values for both SCL and HR, respectively. The analyses were separately performed on the data obtained in each experimental condition: positive, negative and neutral (see section 2.1 a). Results reveal that, for the positive condition, no significant differences were found between the baseline and emotional state SCL values (t(9)= -1.756; ρ= .113), whereas a significant increase in HR values (t(9)= -7.475; ρ= .0001) was recorded. On the other hand, for the negative condition, a significant increase in SCL values (t(10)= -2.797; ρ= .019) emerged, while no significant changes were found in HR values (t(10)=2.154; ρ= .057).These results indicate that positive and negative emotional states produce different patterns of physiological responses. No significant changes in both SCL (t(10)= -.067, ρ= .948) and HR (t(10) =-1.026, ρ=.325) values occurred for neutral condition. To evaluate the effect of the induced emotional state on memory task scores, a oneway ANOVA analysis was performed on the data, considering the experimental condition as fixed factor, and the memory task score as dependent variable. The ANOVA shows that participants’ performances at the memory task were not affected by the emotion induction (F(2,31)=1.288, ρ=.291). However, when ANOVAs (as described above) were performed on data from female and male participants separately, they showed a significant effect of the induced emotional state only for female subjects (Females: F(2,10)=6.258, ρ=.023; Males: F(2,20)=1.150, ρ=.339). In particular, as displayed in Figure 2, post hoc comparisons using the Bonferroni test indicated that females memory task scores, for the negative condition, were sig-

nificantly lower than scores for the neutral condition. Whereas, the results for positive condition did not significantly differ from those for neutral and negative conditions. Finally, linear regression analyses were performed to verify the existence of a significant relation between physiological emotional activation (changes in SCL and HR values) and participants’ memory task performances. The analyses were computed on the data obtained in the three experimental conditions separately. Differences between physiological values (SCL and HR, separately) detected in the baseline and emotional states were considered as independent variables, and memory task scores as dependent variable. Results indicate a barely significant effect related to SCL values in the positive condition (β=.639; t(1)=2.35, ρ=.047) (cf. Fig.3). 25,00

Bonferroni Test Results *

20,00

15,00

10,00

5,00

0,00 Positive

Negative

Neutral

Fig. 2 Means and standard deviations on memory task scores provided by female participants in the 3 experimental conditions. The star refers to significant differences (ρ

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